184 Lakes of the World Through Space and Time: Archives of Climate, Paleoenvironments, Ecosystems, Geohazards, and Economic Resources (Posters)
This session celebrates lacustrine research across the globe. Lake sediments are excellent archives of changing climate, paleoenvironments, human impacts, and economic resources. This session explores limnogeological research on all time and spatial scales.
Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Reconstructing Lake Stratification and Anoxia Using Iron Geochemistry.
Paper number: 184-3
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
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Ioan LascuSmithsonian National Museum of Natural History, Washington, DC
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Elizabeth SwannerIowa State University, Dept. of Geol. & Atm. Sciences, Ames, IA
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Sajjad AkamSmithsonian National Museum of Natural History, Washington, DC
Abstract
Increasing deoxygenation in lakes is a major threat to lake ecosystems, often contributing to meromixis—permanent stratification that results in persistent anoxia in bottom waters. Globally, the number of meromictic lakes has increased over the past two centuries, driven by climatic and anthropogenic land use changes. Sediment records from meromictic lakes offer valuable paleoenvironmental insights into the timing and biogeochemical dynamics of induced hypoxia.
We investigated the redox history of Brownie Lake, an iron (Fe)-rich urban lake in Minnesota, USA, that became meromictic roughly a century ago. A 1.3-meter sediment core, dated from 1828 to 2022, was analyzed at ~5 cm intervals. Each sample was divided into four aliquots to assess the distribution of Fe in (i) organic matter (Feorg), (ii) pyrite (Fepy), (iii) carbonates (Fecarb), oxides (Feox), magnetite (Femag), and (iv) total Fe pool (Fetot).
Our initial results suggest high Fetot (avg = 2.79 wt%) throughout the sediment core. However, a distinct increase in highly reactive Fe (FeHR = Fepy + Fecarb + Feox + Femag, normalized to dry mass accumulation rates) and Feorg was observed starting between the 1913–1925 period. This period aligns with historical urbanization, railroad construction, and sediment slumping in the Brownie Lake area, key events associated with the onset of meromixis. We observed an average four-fold increase in FeHR accumulation rates, and a two-fold increase in Feorg after the onset of meromixis. These increases likely reflect an enhanced role of reductive dissolution, remobilization, and re-precipitation of sedimentary iron under anoxia. Future work will utilize bulk elemental analysis to distinguish detrital vs authigenic iron phases in the lake. Overall, our efforts demonstrate that Fe distribution in sediment records is a valuable proxy for reconstructing redox conditions in iron-rich aquatic systems.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-413900
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